Boot problem

A few days ago I had a problem loading images created from the meta-sifive repository (branch 2020.04). When I try to load an image on a HiFive Unleashed board, the boot process dies after
SiFive FSBL: 2020-05-19-128f282-dirty
Previously, all created images loaded without errors. The switches on the board are set correctly and have not changed.
When you try to load an image created without any changes or additions (pure meta-sifive), the problem persists.

I have built and booted the 2020.04 fusdk on my HiFive Unleashed board, using an x86_64 Ubuntu 18.04 machine for the build.

I would suggest checking the SDcard. They occasionally fail and stop working. Try mounting it on your x86_64 linux build host and checking partitions and files to make sure you can read the files written to the disk, and that they are the same as the ones written. Or try writing an old image to this SDcard that is known to work and see if it still fails. In general, I would suggest using SDcards as little as possible, e.g. boot the system off an SDcard, mount an NFS disk partition, and do all of your user work on the NFS mounted disk. Or if you have a microsemi expansion card, add nvme and/or sata disks and do the user work there. Also, buy good quality SDcards. We use the bi-color Sandisk Ultra or Extreme SDcards, as we have had the best luck with those.